1. Field of the Invention
The present invention relates to improvements in well tools of the type having slip assemblies for grippingly engaging surrounding cylindrical conduits.
2. Description of the Prior Art
A variety of slip assemblies are shown in the prior art for use with well tools including well packers and liner hangers. These prior art devices are actuated in order to support a cylindrical conduit within the interior bore of a circumscribing conduit, typically the cased bore of a well. The prior art slip gripping mechanisms, in general, featured a plurality of wedge-shaped slip elements carried in circumferentially spaced-apart relationship about a generally conically shaped expander surface on the tool body. The lower surface portions of the slips were slidable over complimentary surfaces on the expander so as to cause wicker teeth on the upper surfaces of the slips to be moved between expanded and contracted positions in response to relative axial movement of the slip elements and expander. This relative movement was induced, for example, by hydraulic or mechanical actuation of telescopingly arranged, axially reciprocal members of the tool to which the slips and expander surface were connected.
One disadvantage of such prior art gripping mechanisms was that the loading imposed by the cylindrical conduit was transmitted radially from the expanders to the slips and radially outward into the surrounding well casing. An improvement to the prior art systems is shown in U.S. Pat. No. 4,711,326, issued Dec. 8, 1987, and assigned to the assignee of the present invention. In that device, a body was made up in the string of cylindrical conduit leading to the well surface which included a plurality of spaced, longitudinal slots. Vertically shiftable slips were carried in the slots by side edges which were designed to engage mating profiles formed in the slots. The slots formed guideways for the slips for shifting the slips upwardly and outwardly relative to the body between a set position engaging the circumscribing conduit and an unset position. That slip gripping mechanism allowed a string of cylindrical conduit to be supported within the interior bore of a circumscribing conduit by distributing the load being supported in a circumferential direction, rather than imposing a radial load, as in the prior art.
Despite the advantages of this improved design, a need continued to exist for a slip gripping mechanism which would distribute the slip loading as uniformly as possible over the gripping surface of the slip in order to minimize the resulting stress in the surrounding casing, especially under high load conditions.
A need has also continued to exist for an improved slip gripping mechanism with an improved geometry designed to reduce the setting force necessary to prevent movement of the slip as load was applied during the setting operation.